1 Biological Molecules

Question 1

What is a monomer? (1)

Answer 1

A monomer is a small repeating unit from which larger molecules are made of.

Question 2

Describe the chemical reaction involved in the conversion of polymers to monomers. (1)

Answer 2

A hydrolysis reaction breaks a chemical bond between the monomers using water.

Question 3

Describe the chemical reaction involved in the conversion of monomers to polymers. (1)

Answer 3

A condensation reaction joins monomers together through a chemical bond and releases water.

Question 4

Explain what is meant by a polymer. (1)

Answer 4

A polymer is a molecule made up of many monomers joined together through a condensation reaction.

Question 5

Describe a biochemical test to show that a non-reducing sugar is present. (3)

Answer 5

Heat the solution with dilute hydrochloric acid and neutralise with sodium hydrogencarbonate.

Heat with Benedicts solution.

If the solution turns red, a non-reducing sugar is present.

Question 6

Describe and explain two features of starch that make it a good storage molecule. (2)

Answer 6

It is insoluble in water so the water potential is not affected.

Branched chains so it is compact.

Question 7

Describe the structure of glycogen. (2)

Answer 7

It is a polysaccharide, made up of alpha glucose molecules joined by glycosidic bonds.

Question 8

Name the monomers from which a maltose molecule is made. (1)

Answer 8

Glucose and glucose.

Question 9

Name the type of chemical bond that joins the two monomers to form maltose. (1)

Answer 9

Glycosidic

Question 10

Explain one way in which starch molecules are adapted for their function in plant cells. (2)

Answer 10

It is insoluble so does not affect the cell’s water potential.

Question 11

Explain how cellulose molecules are adapted for their function in plant cells. (3)

Answer 11

They have long and straight chains which become linked by hydrogen bonds, forming fibrils. These provide strength to the cell wall.

Question 12

Name the group represented by COOH. (1)

Answer 12

Carboxyl

Question 13

Describe how you would test for the presence of a lipid in a liquid sample of food. (2)

Answer 13

Add ethanol and shake. then add water and shake again. A white emulsion will indicate the presence of a lipid.

Question 14

Describe how a triglyceride is formed. (3)

Answer 14

One glycerol molecule and three fatty acids are joined by condensation reactions with the release of three water molecules, forming ester bonds.

Question 15

Describe how an ester bond is formed in a phospholipid molecule. (2)

Answer 15

A condensation reaction between a glycerol molecule and a fatty acid forms an ester bond between them.

Question 16

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst. (3)

Answer 16

The substrate binds to the active site. The active site changes shape so it is complementary to the substrate, reducing the activation energy and acting like a catalyst.

Question 17

A competitive inhibitor decreases the rate of an enzyme controlled reaction. Explain how. (3)

Answer 17

An inhibitor of similar shape binds to the active site, preventing an enzyme substrate complex from being formed.

Question 18

Describe how the structure of a protein depends on the amino acid it contains. (5)

Answer 18

The structure is determined by the position of the amino acids.

The primary structure refers to the sequence of amino acids.

Then, the secondary structure refers to the structure formed by the hydrogen bonds, resulting in either an alpha helix or beta pleated sheet.

The tertiary structure refers to the interactions between the R groups resulting in ionic bonds, hydrogen bonds or disulfide bridges.

This creates active sites in enzymes.

The quaternary structure contains one or more polypeptide chain joined together.

Question 19

Describe a biochemical test to confirm the presence of protein in a solution. (2)

Answer 19

Add biuret reagent to the solution. If the solution turns purple, a protein is present.

Question 20

Describe how a peptide bond is formed between two amino acids to form a dipeptide. (2)

Answer 20

A condensation reaction between amine group and carboxylic group form a peptide bond.

Question 21

Describe the structure of DNA. (5)

Answer 21

DNA is a polymer of nucleotides.

Each nucleotide is made up of a deoxyribose sugar, a phosphate group and a nitrogenous base, either adenine, guanine, cytosine or thymine. Between each pair of bases, there are hydrogen bonds.

They have phosphodiester bonds between the nucleotides.

The two polynucleotide strands are held by hydrogen bonds. These form a double helix shape.

Question 22

Describe how a phosphodiester bond is formed between two nucleotides within a DNA molecule.

Answer 22

A condensation reaction between the phosphate and deoxyribose sugar, catalysed by DNA polymerase.

Question 23

Describe the role of DNA polymerase in the semi-conservative replication of DNA. (2)

Answer 23

DNA polymerase joins the adjacent nucleotides and catalyses the condensation reaction between the adjacent nucleotides, forming a phosphodiester bond.

Question 24

Describe two differences between the structure of a tRNA molecule and the structure of an mRNA molecule. (2)

Answer 24

Any two of these four for two marks
- tRNA is folded into a ‘clover leaf’ shape, whereas mRNA is linear.
- tRNA has hydrogen bonds, mRNA does not.
- tRNA has amino acid binding site, mRNA does not.
- tRNA has anticodon, mRNA has codon.

Question 25

Describe the function of each of these enzymes :

DNA Helicase

DNA Polymerase

(2)

Answer 25

DNA Helicase - unwinds the DNA, breaking hydrogen bonds between the bases.

DNA Polymerase - joins adjacent nucleotides via phosphodiester bond.

Question 26

Contrast the structures of ATP and a nucleotide found in DNA to give two differences. (2)

Answer 26

• ATP has ribose and nucleotide from DNA has deoxyribose sugar.
• ATP has three phosphate groups and DNA nucleotide has one phosphate group.

Question 27

Describe how an ATP molecule is formed from its component molecules. (4)

Answer 27

ATP is made up of an adenine group, a ribose or pentose sugar and three phosphates.
A condensation reaction occurs

Question 28

State and explain the property of water that can help to buffer changes in temperature. (2)

Answer 28

Water has a high specific heat capacity. It can gain a lot of energy without changing temperature.

Question 29

Name the two products of ATP hydrolysis. (1)

Answer 29

• Adenosine Diphosphate (ADP)
• Inorganic phosphate (Pi)

Question 30

Describe a biochemical test to show that X solution contains a non-reducing sugar. (3)

Answer 30

Heat the solution with acid and neutralise.
Then, heat the solution with Benedict’s solution.
If a non-reducing sugar is present, the solution will turn red in colour.

Question 31

Describe the roles of iron ions, sodium ions, and phosphate ions in cells. (5)

Answer 31

Haemoglobin binds with oxygen. (iron ions)
Co-transport of glucose into cells because the Na ions are moved out by active transport.
This creates a sodium concentration gradient, affecting water potential.
(sodium ions)
Phosphate ions joins nucleotides in the backbone of DNA/RNA. They are used to produce ATP.
(phosphate ions)

Question 32

The movement of substances across cell membranes is affected by membrane structure. Describe how. (5)

Answer 32

Phospholipid bilayer allows movement of lipid soluble substances across the membrane.
Phospholipid bilayer prevents movement of lipid insoluble substances across the membrane.
Carrier proteins allow for active transport of ions across the membrane.
Cholesterol affects the permeability of the membrane.
Channel proteins allow for facilitated diffusion of substances across the membrane.